1. Field of the Invention
The invention relates in general to hoist ring assemblies and, in particular, to hoist ring assemblies which are largely formed by forging and are assembled as forged.
2. Description of the Prior Art
Hoist rings have been widely used in industry to provide attachment points on heavy objects so that tools such as hoists, cranes and jacks may be applied to lift the heavy objects. Hoist rings are generally considered to be critical safety items because if a malfunction occurs, a heavy object may be dropped with resultant damage to people, the object, and its surroundings. Accordingly, hoist rings have generally been carefully manufactured with machined mating surfaces to maintain relatively close tolerances.
It is well known that machining operations are expensive in time and materials. Forgings are much quicker and easier to produce with substantially less waste material. It is not possible, however, to hold close tolerances on forged parts. For reasons of strength, the various components in a hoist ring assembly have generally been manufactured by forging operations. The components produced by forging have been considered to be blanks from which the final mating surfaces have been machined to the desired tolerances. It has generally been considered impractical to attempt to assemble the hoist ring assembly components in the as forged condition. Typical tolerances for as forged components are plus or minus sixty thousandths of an inch or more while those for machined parts are plus or minus five thousandths of an inch or less.
Previous hoist ring or eye-bolt assemblies included, for example, those disclosed in Tsui et al., U.S. Pat. No. 4,641,986, patented Feb. 10, 1987. The frusto-conical mating surfaces disclosed there between the pivot pins and the bearing recesses must be machined in order to maintain the required tolerances. The spherical pin ends disclosed there are very difficult to form by forging alone so, a machining operation is necessary to achieve the desired configuration.
These and other difficulties of the prior art have been overcome according to the present invention.